I specifically investigate the effect of prenatal morphine exposure on the postnatal neuronal development in the nucleus accumbens (NAc), one of the critical brain regions involved in the motivation and reward. I first examined the intrinsic properties of D1- and D2-MSN in the vehicle control and found a decline in the membrane excitability during postnatal second to fourth weeks. In contrast, pups experienced prenatal morphine exposure delayed the developmental pattern and showed a higher excitability during this period. When examined in the excitatory synaptic responses, prenatal morphine treatment delayed developmental trend particularly in the postsynaptic responses. Taken together, my results suggested the prenatal morphine exposure not only delay the intrinsic properties development of D1- and D2-MSN, but also affect excitatory synaptic connection during early postnatal period. Whether these alterations contribute the drug seeking behaviors during adulthood will further be investigated.